Manufacture of diolefins



- June 3, 1947.- I R N 2,421,50

MANUFACTURE OF DIOLEFINS Filed July 28, 1941 DIOLEFIN HYDROGEN RECYCLE PARAFFINS & OLEFINS SEPARATING MEANS INVENTOR JEAN F? JONES Patented June 3, 1947 2,421,506, MANUFACTURE or DIOLEFlNS Jean P. Jones, Bartlesville, Okla, asslgnor to I Phillips Petroleum Delaware Company, a corporation of Application July 28,1941, Serial No. 404,420 I 1 This invention relates to the production of diolefin hydrocarbons by dehydrogenation. It relates more particularly to the production of such diolefins by means of catalytic dehydrogenation wherein unreacted hydrocarbons comprising parafiins and olefins are recycled to a dehydrogenation step. The invention has particular reference to the production of diolefins such as butadiene, pentadiene and isoprene from the corresponding paraflin hydrocarbons and of cyclopentadiene from cyclopentane, preferably .by means of catalytic dehydrogenation.

It has been proposed to produce diolefins by dehydrogenation in a single step wherein a paramn hydrocarbon such as normal butane is charged to the dehydrogenation step, a diolefin such as butadiene is recovered from the dehydrogenation efliuent, and a hydrocarbon fraction containing unreacted hydrocarbons, such as normal butane and butenes, are separated from the eiiluent and 8 Claims. "(CL 260-680) from paraifin hydrocarbons returned to the dehydrogenation step. It has Q also been proposed to produce diolefins from paraffin hydrocarbons by the use of at least two dehydrogenation steps in the first of which paraffins are dehydrogenated to'oleflns and in the second of which olefins are dehydrogenated to diolefins. In such a process there is generally a recycle of unreacted hydrocarbons to one or more of the dehydrogenation steps. In preparing the charge to such dehydrogenation processes it is impossible from a practical point of view to separate a hydrocarbon material such as normal butane in a state of high purity, and in most instances when the particular desired hydrocarbon is present in a concentration of about 95 per. cent or more, it is considered to be in a sumciently high state of purity for practical operations. At times the concentration may even be somewhat lower than 95 per cent although generally it will not be appreciably lower than about 90 per cent. Also in such dehydrogenations there. is a. tendency for isomeric forms of the hydrocarbons being treated to be formed as byproducts in the dehydrogenation step. Thus, in

the dehydrogenation of normal butane and/or normal butenes to form butadiene, there is a tendency for small amounts of isobutene and isobutane to be formed. When a hydrocarbon fraction containing unreacted hydrocarbons is recycled to the dehydrogenation step, it will contain such isomeric hydrocarb ns in either case, and as a result after a steady state of operation has been reached, the total charge to a dehydro= genation step will contain a substantial amount of such isomeric hydrocarbons which do not contribute directly to the production of the desired diolefins which not only decrease capacity of the dehydrogenation units but also tend to enter into undesired side reactions.

I have -now found that this tendency for isomoving from the hydrogenation eflluent the desired paraflin hydrocarbon and returning such a desired paramn hydrocarbon to the dehydrogenation system. This procedure may be followed either when the undesired isomeric hydrocarbons are present as a, result of formation within the dehydrogenation system or when they are present as a result of being included as impurities as a charge to the dehydrogenation system or for any other reason.

An object of my invention is to produce diole- V fin hydrocarbons.

. It is an object of my invention to produce lowboiling dlolefln hydrocarbons from paraflin hydrocarbons of the same number of carbon atoms per molecule.

It is a further object of my invention to produce diolefin hydrocarbons by means of catalytic dehydrogenation of more saturated hydrocarbons under conditions such that there is a, minimum formation of undesired by-products.

Further objects and advantages of this invention will become apparent from the accompanying disclosure and discussion.

My invention will now be described in connection with the accompanying drawing which shows diagrammatically-by way of a. flow sheet an arrangement of apparatus for practicing my invention together with certain modifications thereof. The description of my invention in connection with the drawing will also serve to exemplify the same.

Referring now to the drawing, a suitable hydrocarbon material enters the system through a, pipe l0 controlled by a valve li and is passed to a separating means illustrated by the fractionating column l2. Preferably such a hydrocarbon mixture will comprise predominantly hydrocarbons of a single number of carbon atoms low-boiling hydrocarbons are discharged from the system through a pipe l3 controlled by a valve l4, and any undesired high-boiling material is discharged through a pipe I9, controlled by valve 29. A normal butane fraction of as high a purity as is practical, and preferably-containing normal butane as at least 95 per cent of the mixture, is removed through a, pipe l5 controlled by a valve l6 and may be passed through a valve l1 directly to a single dehydrogenation unit I8. The dehydrogenation unit I8 is comprised of suitable heating units or furnaces, catalyst chambers and the like known to the art for effecting and maintaining catalytic nondestructive hydrogenation of low-boiling hydrocarbons. Th catalyst chambers may be so arranged that heat -is supplied to the catalyst body o bodies and to the reacting mixture. Whena single dehydrogenation unit is used, the dehydrogenation is conducted to effect a dehydrogenation both of parafiins and of olefins to form olefins and diolefins, respectively, along with free hydrogen. The resulting products passthrough a pipe controlled by a valve 2| to separating means 22. Separating means 22 will include suitable fractionating columns, condensing units, heat exchangers, solvent extraction units and the like suitable for effecting a separation of the material charged into the desired fractions a will be discussed. A diolefln fraction, in this case containing a high concentration of butadiene, is recovered as a product of the process from separating means 22 through a pipe 23 controlled by a valve 24. A fraction containing light gases with a high concentration of free hydrogen formed by the dehydrogenation is removed from separating means 22 through a pipe 25 and may be discharged at least in part from the system through a valve 26. Any undesired heavy material may be discharged from the system through a pipe 2! controlled by a valve 28. A recycle fraction, which in this case will comprise predominantly normal butane and normal butenes, is removed from separating means 22 through a pipe and a substantial portion thereof, preferably a predominant portion, is passed through valve 3! to be returned to the dehydrogenation unit l8. As discussed, this recycle fraction will contain appreciable amounts of isomeric hydrocarbons, in this case isobutane and isobutene. In accordance with the invention a portion of the recycle material passing through pipe 30 is passed therefrom through a pipe 32 and is passed through valve 33 to a hydrogenation unit 34. Any undesired portion of this stream may be discharged from the system through pipe 35 controlled by a valve 36. Hydrogen in an amount sufiicient to effect a substantially complete saturation of unsaturated material charged to hydrogenation unit 34 is added to the system through a pipe 31. This hydrogen may be added entirely or in part through a valve 38, but generally there will be more than sufficient hydrogen in the stream discharged through pipe 25 to suflice for this operation, and any desired portion of this stream may be passed from'pipe 25 througha pipe 40 controlled by a valve 4| to pipe 31 and hydrogenation unit 34. V

The hydrogenation in unit 34 will be one of simple nondestructive substantially complete saturation of unsaturated hydrocarbons charged thereto and may be carried out in the presence of an active hydrogenation catalyst, such as finely divided nickel on an inert support such as pumice, silica gel, or the like, under a suitable pressure and temperature. Such temperature and pressure will generally not need to be greatly elevated and conditions for any particular stock being treated may be readily determined by trial by one skilled in the art. The effluent of the hydrogenation is passed from unit 34 through a pipe 42 controlled by a valve 43 to a, separating means 44. Any undesired low-boiling material such as unreacted free hydrogen and hydrocarbons of a fewer number of carbon atoms than the material treated in the dehydrogenation unit l8 may be discharged from the system through a pipe 45 controlled by a valve 46. A parafiin hydrocarbon fraction preferably predominantly of a single number of carbon atoms per molecule, in this case a butane fraction, is recovered through a pipe 41 and is passed through valve 48 to pipe l0 and fractionatin unit l2.

In some instances it may be desired to conduct the dehydrogenation operation in two or more steps; in such an event the stream passing through pipe I5 will be passed therefrom through pipe 50 controlled by a valve 5| to a dehydrogenation unit 52' which as in the case of dehydrogenation unit I 8 is comprised of suitable heating units or furnaces, catalyst chambers and the like known to the art for effecting and maintaining catalytic nondestructive dehydrogenation of low-boiling hydrocarbons. The material charged to dehye drogenation unit 52 should be predominantly paraflinic, and the dehydrogenation conditions should be such that there is an optimum formation of mono-olefins of the same number of carbon atoms per molecule as the paraffins charged. The dehydrogenation effluent is passed through'the pipe 53 controlled by valve 54 to separating means 55. A fraction containing the desired olefins produced by the dehydrogenation is removed from separating means 55 through a pipe 56 controlled by a valve 51 and is passed back to pipe I5 for introduction to dehydrogenation unit [8. With such an operation valve I! in pipe l5 will be closed. Undesired low-boiling materials, including free hydrogen produced by the dehydrogenation, may be discharged from the system from the system through pipe 58 controlled by a valve 59 passing from separating means 55. Free hydrogen contained in this stream may be used in the hydrogenation unit 34, and if such use is desired th hydrogen may introduced through valve 38 as will be readily appreciated. In some instances the material passing th'roughpipe 56 will contain substantially all of the unreacted paraffin charged to dehydrogenation unit 52, in which case separating means 55 can be operated simply to separate a hydrocarbon fraction such as a butane-butene fraction from lower boiling material. However, in some instances it may be found desirable to have a high concentration of olefins in the material charged ,to dehydrogenation unit l8. In such a ,case separating means 55 will also include suitable equipment for separating olefins from paraifins, such as selective solvent extraction equipment as will be readily appreciated by those skilled in the art. Paraflln hydrocarbons separated in such a manner may be returned to de- 7 hydrogenation unit I2 as through pipe '0 controlled by a valve ii. In some. instances with either modification of the dehydrogenation system, material charged through pipe ill may contain substantially only hydrocarbons of a single carbon atom skeleton structure and may in such a case constitute the sole charge to the process.

When a fraction containing a high proportion of.

olefins suitable for dehydrogenation into diolefins is available from any outside source such a material may be charged to ,the system through pipe 60 when dehydrogenation unit It is the only process through pipe 62 controlled by a valve 83 passing into pipes Illand I5 directly to dehydrogenation unit l8, and in some instances material charged through pipe 62 may constitute the sole charge to the process.

It has previously been mentioned that the dehydrogenation carried out in units 18 and/or 52 will be conducted under conditions known to the art and will generally be conducted under a relatively low pressure with or without the presence of diluent material such as hydrocarbons inert under the dehydrogenation conditions, nitrogen, steam, carbon dioxide and the like. Sometimes introduction of small amounts of free hydrogen along with the charge to a catalyst bed has a beneficial efiect, especially upon the initial portion of a catalyst bed before hydrogen is produced by dehydrogenation, and the presence of such added hydrogen does not retard unduly or upset the dehydrogenation reaction. Such in-" troduction can be made for example, through pipe 60 and/or pipe 62. Any of various dehydrogenation catalysts may be used, among which the more preferred are alumina and/or chromium oxide catalysts such as bauxite, bauxite treated with other materials such as an alkali or alkaline earth oxide, as barium oxide, unglowed chromium oxide, alone or in admixture with other oxides, and prepared from a gelatinous chromium hydroxide, from carefully controlled. low temperature decomposition of an ammonium chromate, and the like. Suitable dehydrogenation temperatures will generally be found in the range of 800 to 1300 F. A single stage dehydrogenation, as first described in connection with dehydrogenation unit It, is preferably carried out with a, catalyst comprising chromium oxide, or chromium oxide and alumina, at a temperature in the range of 950 to 1100 F., while a two-stage operation may be carried out with a similar catalyst under slightly less drastic time-temperature conditions in dehydrogenation unit 52, with subsequent dehydrogenation of resultant oleflns at a higher temperature, such as within the range of 1050 to 1250 F., using a catalyst such as bauxite treated with barium hydroxide, 'or temperaturestabilized chromium oxide, with or without the presenceof steam, or the like, as diluent. In all such dehydrogenation steps low pressures,

passed to the hydrogenation unit 34 will depend I on the degree of purity of the stock charged to," the dehydrogenation unit or units, and on the isomerizing characteristics o1!v the dehydrogenation conditions. With less pure stocks and/or appreciable tendencies to form isomeric hydrocarbons, a larger portion will need to be passed to the hydrogenation step than with more favorable conditions. Generally the amount so treated will be at least about 5 per cent of the total recycle stream, and while it may be as high as about 25 per cent, it will generallybemore economical to modify other conditions to obtain more favorable operation than to operate so that more than about 15 per cent is so treated. Suitable ratios in any particular case can be readily determined by one skilled in the art.

Pumps or compressors for the various streams inconnection with the drawing have not been shown; general flow of the various streams, however, has been" indicated and discussed, and suitable mechanical equipment for desired treatment I of this material can be readily supplied, as required in any particular modification of my invention, by one skilled in the art. Similarly other units of equipment have been shown only diagrammatically but their functions have been described and explained so as to serve as suitable guides for adaption of suitable specific equipment or specific installations. It will be obvious to those skilled in the art that various modifications of my invention may be practiced as being included in the spirit of the disclosure and in the scope of the claims. In the present specification and claims when it is stated that a portion pentane fraction'and an isopentane fraction each which may. be subatmospheric but which generalments of G5 hydrocarbons are substantially with' in the same ranges, with slightly lower temperatures in otherwise comparable cases.

The amount of the paraffin-olefin mixture which, in any particular. case; is removed and of which may be treated under conditions'optimum for the production of the corresponding diolefln. In such'a case the products of hydrogenation oi the fractions removed from the recycle stream in each of the diolefln production systems may be combined and recharged to the fractionating unit I2 as will be readily appreciated.

Iclaim:

1. A process for the production of butadiene, which comprises catalytically dehydrogenating a normal C4 fraction containing normal butane and normal butenes, separating from the eilluent of said dehydrogenation butadiene, separating also a normal, 04 fraction substantially free of butadiene and containing a minor amount of iso- C4 hydrocarbons and including olefins returning a portion of said 04 fraction to said dehydrogenation, subjecting a further portion of said C4 fraction to nondestructive hydrogenation to form a paraiiinic fraction, separating a normal butane fraction from said paraflinic fraction, and introducing said normal butane fraction into the dehydrogenation system. I

2. A process for the production of a low-boiling diolefln, which comprises catalytically dehy-e drogenating a low-boiling hydrocarbonfraction When a pentane fraction is charged to singlecarbon skeleton and of four to five carbon' atoms in a straight chain to form a corresponding diolefin, separating from the efiluent of said dehydrogenation a diolefin fraction containing diolefins so produced and recovering same as a product of the process, separating also a hydrocarbon fraction comprising olefins substantially free of diolefins and containing hydrocarbons of the same number of carbon atoms per molecule as comprise said low-boiling fraction, and both the same and different carbon atom skeleton structure passing a major portion of said diolefinfree fraction to said dehydrogenation, subjecting a minor portion of said diolefin-free fraction to nondestructive hydrogenation to form a parafllnic fraction, separating from said parafiinic fraction paraffins having a carbon skeleton different from the first hydrocarbons, and passing hydrocarbons remaining in said paraifinic fraction to said dehydrogenation.

3. A process for the production of a low-boiling diolefin, which comprises passing a low-boiling hydrocarbon mixture containing predominantly parafiin hydrocarbons of four to five carbon atoms per molecule to a fractionating means, separating therefrom a low-boiling paraffinic fraction comprised substantially of hydrocarbons of a single carbon atom skeleton and containing from four to five carbon atoms in a straight chain, passing said fraction to a dehydrogenation system to effect a dehydrogenation thereof forming diolefins, separating from an efliuent of said dehydrogenation system a diolefin fraction as a product of the process, separating also a fraction comprising olefins substantially free of diolefins and containing hydrocarbons of the same number of carbon atoms per molecule as comprise said low-boiling parafiinic fraction, and both the same and different carbon atom skeleton structure passing a major portion of said separated fraction to said dehydrogenation system, subjecting a minor portion of said separated fraction to nondestructive hydrogenation to saturate unsaturated hydrocarbons contained therein forming a paraflinic fraction, and passingsaid resultant parafiin hydrocarbon fraction so produced to said fractionating means.

4. A process for the production 'of butadiene, which comprises passing a butane-containing mixture to a fractionating means, separating therefrom a normal butane fraction, passing said normal butane fraction to a dehydrogenation system to effect a dehydrogenation thereof forming butadiene, separating from an efiluent of said dehydrogenation system a butadiene fraction as a product of the process,'separating also a fraction containing free hydrogen, and separating further a normal-C4 fraction substantially free from butadiene and containing a minor amount of iso-C4 hydrocarbons and including olefins, passing a portion of said normal-C4 fraction to said dehydrogenation system, subjecting a further portion of said normal-C4 fraction to nondestructive hydrogenation in the presence of free'hydrogen from said fraction containing free hydrogen to form a parafiinic fraction containing normal butane, and passing said parafifinic fraction to said fractionating means.

5. A process for the production of piperylene,

which comprises passin a pentane-containing mixture to a fractionating means, separating therefrom a normal pentane fraction, passing said normal pentane fraction to a dehydrogenation system to effect a dehydrogenation thereof forming piperylene, separating from an efliuent,

of said dehydrogenation system a piperylene fraction as a product of the process, separating also a fraction containing free hydrogen, and separating further a normal-C5 fraction substantially free of piperylene and containing a minor amount of iso-Cs hydrocarbons and including olefins, passing a portion of said normal-C5 fraction to said dehydrogenation system, subjecting a further portion of said normal-C5 fraction to nondestructive hydrogenation in the presence of free hydrogen from said fraction containing free hydrogen to form a paraffinic fraction containing normal pentane, and passing said paraffinic fraction to said fractionating means.

6. A process ,for the production of isoprene, which comprises passing a pentane-containing mixture .to a fractionating means, separating therefrom an isopentane fraction, passing said isopentane fraction to a dehydrogenation system to efiect a dehydrogenation thereof forming isoprene, separating from an eflluent of said dehydrogenation system an isoprene fraction as a product of the process, separating also a fraction containing free hydrogen, and separating further an iSO-Cs fraction substantially free of isoprene and containing a minor amount of normal-C5 hydrocarbons and including olefins, passing a portion of said iso-Cs fraction to said dehydrogenation system, subjecting a further portion of said iso-Cs fraction to nondestructive hydrogenation in the presence of free hydrogen from said fraction containing free hydrogen to form a parafiinic fraction containing isopentane, and passing said parafiinic fraction to said fractionating means.

7. A process for the production of a diolefin from a more saturatedhydrocarbon containing from four to five carbon atoms per molecule and having the same carbon atom skeleton structure as said diolefin, which comprises subjecting said hydrocarbon to catalytic dehydrogenation to dehydrogenate said hydrocarbon forming the corresponding diolefin, separating from an effiuent of said dehydrogenation the diolefin so produced, separating also a hydrocarbon fraction comprising olefin hydrocarbons having the same number of carbon atoms per molecule as the first said hydrocarbon and boththe same and difierent carbon atom skeleton structure, passing a portion of said hydrocarbon fraction to said dehydrogenation step, subjecting a further portion of said hydrocarbon fraction to nondestructive hydrogenation, separating from the hydrogenation efiluent a paraflinic fraction of the same carbon atom skeleton structure as the first said hydrocarbon, and passin said parafiinic fraction to the dehydrogenating step.

8. An improved process for the conversion of normal butane to butadiene, which comprises passing a mixture comprising normal butane and isobutane to a fractionating means, separating therefrom a normal butane fraction, passing said normal butane fraction to a first catalytic dehydrogenation step and therein subjecting said normal butane to dehydrogenation conditions to produce normal butenes, separating from efiluents of said first dehydrogenation step a fraction com-' prising normal butenes, passing said fraction to a second dehydrogenation step and therein subjecting said normal butenes to dehydrogenation conditions to produce butadiene, separating from efliuents of said second dehydrogenation step a butadiene fraction containing butadiene so produced and recovering same as a product of the process, separating also from the last said efllu- 9 ents a fraction'containlng free hydrogen, separating also from the last said eflluents a hydrocarbon fraction substantially free of butadiene and containing unreacted butenes together .with a minor amount of isobutylene, passing a major portion of said butadiene-free fraction .to said second dehydrogenation step, passing a minor portion of said butadiene-free fraction to a nondestructive hydrogenation step and nondestructlvely hydrogenating said minor portion in the presence of free hydrogen from said fraction containing free hydrogen to form a paraflimc hydrocarbofi fraction containing normal butane and isobutane, and passing said paraflinic fraction to said fractionating means.

JEAN P. JONES.

The following references are of record in the file of this patent:

REFERENCES CITED N 'umber FOREIGN PATENTS Country Date Great'Brltain July 5, 1939 

